$100 million in work planned to bolster three New Orleans canals

Ted Jackson / The Times-Picayune archiveThe Corps of Engineers plans to strengthen the floodwall on the London Avenue Canal.

The Army Corps of Engineers plans to drive steel sheet piling about 60 feet into the ground along parts of the London Avenue Canal's eastern floodwall -- three to four times deeper than those that catastrophically failed during Hurricane Katrina -- in hopes of significantly increasing the volume of water that the canal can hold.

The project is part of a corps initiative, expected to cost more than $100 million, to raise the "safe water" levels in the London and 17th Street canals by repairing and improving some deficiencies. The money also will go to close a floodwall gap in the more robust Orleans Avenue Canal, which didn't breach in Katrina and already enjoys a higher capacity than the weaker channels.

Increasing safe water levels would reduce the frequency at which corps floodgates must be closed to block storm surges into the canals from Lake Pontchartrain or, in the case of the problematic London canal, from even stiff southerly winds and a heavy rain. There were no restrictions on water levels, and no floodgates, before floodwalls on the London and 17th canals breached during Katrina, inundating much of New Orleans' east bank and part of East Jefferson. More than 1,500 people in Louisiana died.

The corps and its contractors are now drawing up plans to drive the sheet pilings deep in the earth along 2,300 linear feet of the London canal north of the Katrina breach at Mirabeau Avenue, said supervising geotechnical engineer John Grieshaber of the corps' Hurricane Protection Office. The goal is to build a barrier to stop canal water from seeping through the sand layers that underlie the channel and its levees, a problem that forensic investigators have called a principal contributor to two floodwall breaks during Katrina.

"We have identified two areas in London canal that we're putting on a fast track to drive sheet piling to completely cut off the sand strata," Grieshaber said, calling this the first step toward increasing the canal's safe water level from the current 5 feet to 8 feet.

One of the new sections will be 1,300 feet long, the other 1,000 feet,

But Grieshaber said the 2,300 feet represents only 40 to 50 percent of the length that must be fixed to adjust the safe water level.

"We'll still have other areas in the canal where we'll have to do the same thing, but these are the largest continuous sections of (needed) sheet piling that we known of at this point," he said.

'I don't trust those walls'

It remains to be seen what kind of support the plan gets outside of the corps.

Regional levee authority executive Bob Turner, for example, said he can't evaluate the corps' plan yet because he hasn't heard it explained or examined the data on which it is based.

"We certainly want to get the safe water elevations raised, especially in the London where the situation is so difficult," said Turner, an engineer. "But it's premature for me to comment on this until we have an opportunity to look at what the corps has planned and to give them our input."

"They need to redesign the canal and eliminate the need for floodwalls or, at the very least, completely rebuild them ... the right way," he said.

Stradford Goins, an engineer and former corps employee who now serves on the Southeast Louisiana Flood Protection Authority-East, has no faith even in the corps' current designation of 5 feet as safe.

"I don't trust those walls under any circumstance," said Goins, a Mississippi resident whose mother's home on the London Avenue Canal flooded during Katrina.

The need to drive steel sheet pilings deep enough to separate canals from the porous sand that underlies them -- a particularly dangerous situation at London canal -- is one of the most expensive lessons learned from Katrina. Before the 2005 hurricane, the corps in New Orleans didn't require that canal floodwall foundations extend to such depths.

For example, when rising water in the London canal seeped through the sand and breached the east and west floodwalls, the sheet pilings that supported the failed wall sections ranged from 16 to 28 feet deep, according to subsequent forensic investigations and cross section drawings of the breach sites.

Grieshaber said the new curtains to cut off seepage will be driven through the sand layers, which extend 50 to 55 feet down from ground level, and into the clay below.

Some cut off panels also are likely to be needed along the 17th Street Canal, he said. But he suggested that the bulk of work there will focus on increasing floodwall stability. And the likeliest method of doing that is the use of deep soil mixing, in which a special grout is injected underground to strengthen weak soils, Grieshaber said.

Although a remediation plan for the 17th Street Canal, where the current safe water level is 6 feet, has not been devised yet, Grieshaber said press hammers will be used to drive sheet piling near densely populated neighborhoods in hopes of minimizing noise and vibration.

New design standards

Corps contractors began reanalyzing all three canals more than a year ago using, for the first time, all the new design standards that the agency phased in after Katrina to increase floodwall safety. At first, Grieshaber predicted the studies would be finished, and any required work completed, by June 1, 2009.

Indeed, Grieshaber said there is still no consensus on safe water elevations among all design, evaluation and peer review team members who are being consulted on the process. In fact, he said, there isn't unanimous agreement even on the validity of the current 5-foot level at the London canal.

"You could find members of the team who'd take exception to it," he said.

But Grieshaber said there is enough agreement on the need for seepage cutoff in the London canal that the work there, as well as the work to close the gap in an Orleans Avenue floodwall, can move ahead.

He said the corps remains convinced that the existing safe water levels are valid. The new work, he said, is about increasing safe water levels and reducing the frequency of gate closures, which interferes with the normal operation of S&WB pumping stations and burdens internal drainage.

"It's all about getting to 8 feet," he said. "It's about jump-starting these projects while the committee continues its work."